A study of the corrosion resistance of electroplated nanocrystalline and polycrystalline nickel coatings

The corrosion resistance of electroplated nanocrystalline and polycrystalline nickel coatings in neutral 3.5% NaCl and 2N H2SO4 solutions was studied using electrochemical techniques such as polarisation resistance and potentiodynamic polarisation. For comparison purposes, the corrosion behaviour of amorphous nickel plating was also included in the study. In 3.5% NaCl solution, nanocrystalline nickel showed good passivation behaviour and its passive breakdown potential was found to be 200 mV higher than that of the conventional polycrystalline nickel. The amorphous nickel plating showed no significant passive behaviour. In acidic solution, however, nanocrystalline nickel showed higher corrosion current density than that of polycrystalline and amorphous nickel, indicating a greater corrosion rate in acid. It is noteworthy that the nanocrystalline nickel on NdFeB substrate showed a well-defined passive behaviour.